1. Field of the Invention
The present invention relates to a substrate transfer robot and, more particularly, to a substrate transfer robot which can efficiently cool its arms, of which temperature normally rises during operation because the arms are arranged in high-temperature vacuum atmosphere.
2. Description of a Related Art
In recent years, semiconductor processing equipment which performs sheet-fed processing not batch processing has been mainly employed because such equipment can satisfy demands of enhancing the accuracy of wafer products and improving the throughput. FIG. 1(a) is a schematic plan view showing an example of the construction of a sheet-fed processing equipment 150. FIG. 1(b) is a partial sectional side view thereof. The sheet-fed processing equipment 150 comprises a transfer chamber 151 having hexagonal plan view, and a plurality of loading air locks 152 and a plurality of process chambers 153 (only parts thereof are shown) are connected to the transfer chamber 151 via connecting flanges 158 such that the loading air locks 152 and the process chambers 153 are arranged radially about the transfer chamber 151. These chambers 151, 153 are sealed with high tightness by shut-off valves 154 provided on the connecting flanges 158 and are vacuumed of a high degree by a vacuum pump, not shown. Treatments for wafers are all performed in a vacuum atmosphere.
Each loading air lock 152 receives a cassette 171 in which wafers processed or to be processed are accommodated. Disposed in the process chambers 153 are respective devices (not shown) for processing the wafers. In the sheet-fed processing equipment 150, the wafers are transferred among a plurality of the process chambers 153 whereby the wafers are continuously subjected to a plurality of processes.
The construction of the substrate transfer robot 160 will be described in detail with reference to FIGS. 2, 3. A sectional view of FIG. 2 shows the substrate transfer robot 160 of a three-axial cylindrical coordinate type, with a part being broken away for illustrating the inside construction thereof. FIG. 3 is a plan view showing arms accommodated inside the transfer chamber 151. Shown in FIGS. 2, 3 is the substrate transfer robot in a state that the end of an end effector 163 as one of the arms extends into the process chamber, not shown, adjacent to the transfer chamber 151 via the connecting flange 158.
The substrate transfer robot 160 is fixed to an opening 151a formed in the bottom of the chamber via a attachment flange 155 such that the arms are positioned within the transfer chamber 151. The transfer chamber 151 is a polygonal-column-shaped vessel and has a roof plate 156 on the top thereof to keep air tightness. The substrate transfer robot 160 comprises, as shown in FIG. 3, a first arm 161, a second arm 162 which is attached to the end of the first arm 161 and is rotatable independently of the rotation of the first arm 161, and the end effector 163 which is attached to the end of the second arm 162. Therefore, the substrate transfer robot 160 can perform the forward and reverse rotation (.theta.) about the center of a robot shell 165, the radial movement (R) of each arm end with the rotation of each arm by the rotation of the rotational axis of the arm transferred through a transmission housed in the arm, and the vertical movement of each driving shaft (see FIGS. 1(a), 1(b)).
As shown in FIG. 2, predetermined rotation is applied to the arms 161, 162, and the end effector 163 of the substrate transfer robot 160 by driving shafts 167, 168 which are arranged coaxially to each other. The rotation of a drive motor (not shown) arranged within the robot shell 165 is transmitted to the driving shaft 167, 168 through a reduction gears (not shown) in a lower bearing box 166. The first driving shaft 167 is a solid steel shaft and is housed in the second driving shaft 168 of a hollow tube type. The second driving shaft 168 of a hollow tube type is arranged coaxially with the central axis of the robot shell 165 to rotate independently of the first driving shaft 167. The upper end of the first driving shaft 167 extends through an upper bearing portion 169 for the first arm 161 and is fixed to a bearing flange (not shown) of the first arm 161. Therefore, the rotation of the first driving shaft 167 is directly transmitted to the first arm 161, thereby rotating the first arm 161 corresponding to the rotational angle of the first driving shaft 167.
On the other hand, the driving transmitting mechanisms of the second arm 162 and the end effector 163 will now be described, but not shown. Fixed to the upper end of the second driving shaft 168 positioned outside of the bearing flange of the first driving shaft 167 is a timing pulley. A timing belt (not shown) is disposed inside the first arm 161 and is stretched between the timing pulley and the rotational shaft of the second arm 162. As the first driving shaft 167 is rotated independently of the second driving shaft 168 to rotate the first arm, the rotational shaft of the second arm 162 is rotated through the timing pulley fixed to the second driving shaft 168 and the timing belt inside the first arm. Therefore, the second arm 162 can be rotated in the reverse direction at a ratio of 1:2 to the rotational angle of the first arm 161 i.e. by double the angle of the first arm 161. Outside of the rotational shaft of the second arm 162, another timing pulley is fixed to the first arm 161 independently of the rotational shaft of the second arm 162. The timing pulley drives the end effector 163 at the end of the second arm 162 through a belt. The rotation of the timing pulley is transmitted to a rotational shaft at the other end of the second arm 162 through the timing belt within the second arm 162 so as to rotate the rotational shaft. The rotation of the rotational shaft moves the end effector 163 fixed to the rotational shaft along a straight line in the transferring direction. The arms structured as stated above are operated according to sequential control. A sequence of operation for the linear transference of the wafers between the loading air lock and the process chamber can be performed.
By the sequential control with the original position where the second arm is superposed on the first arm, the arms and the end effector perform the respective rotation and the telescopic movement whereby the wafers (not shown) can be transferred between the predetermined chambers by the adsorption at the end of the end effector. During this, the valve 154 (see FIG. 1(b)) is opened or closed when the end effector passes the connecting flange 158. Though, for example, a chemical vapor deposition (CVD) process among the substrate processes is performed in relatively low-temperature atmosphere (350-600.degree. C.), a diffusion process may be performed in high-temperature atmosphere about 1200.degree. C. During this process, the end of the second arm and the end effector extending in the process chamber are subjected to radiant heat from the heat source so that heat is stored in the end effector and the arms, increasing their temperature.
Conventionally, to prevent the increase in the temperature of the arms, insulating reflectors for heat reflection are attached on outside walls of the arms. This prevents the arms from being subjected directly to radiant heat, thus preventing the temperature increase in the arms. When the temperature for the process is 1000.degree. C. or more, however, the reflectors as the cooling mechanism become high temperature, not preventing the increase in the temperature of the arms.
The driving shafts for the arms are supported by bearing means such as ball bearings. That is, the driving shafts are connected to the retainer side by point or line contacts with movable bodies such as a plurality of steel balls, rollers, or the like in the bearings. Unlike the normal atmosphere, thermal emission is performed only by heat conduction or radiation in the vacuum atmosphere, so that the efficiency of heat transfer at the point or line contacts of the bearings is quite poor in the case of this construction. Accordingly, heat is hardly emitted from the arms and easily remains in the arms.
To solve this problem, a cooling construction can be thought in which the arms close to the heat source is directly cooled by coolant. That is, in the construction, a circulating piping for the coolant is provided for the moving elements of the arms.
However, to provide such a circulating piping for the coolant in the vacuum atmosphere, it is required to prevent leakage of coolant at joints and pipings. This makes the construction complex and increase the product cost. In addition, it is hard to make the cooling construction to have compact size. Because the pipings should be made of flexible material, problems with regard to the durability occurs, for example, leakage of coolant.
Therefore, it is an object of the present invention to solve the problems of the conventional technique as stated above and to provide a substrate transfer robot in which arms operating in high-temperature vacuum atmosphere are securely cooled.